Spark plug electrode and method of manufacturing the same

ABSTRACT

A spark plug electrode with an electrode tip formed on an electrode base using an additive manufacturing process, such as a powder bed fusion technique. The spark plug electrode includes an electrode base that at least partially surrounds a heat dissipating core, an electrode tip that is formed on the electrode base and includes a precious metal-based material, and a thermal coupling zone that directly thermally couples the electrode tip to the heat dissipating core. In some examples, the electrode tip is formed on an electrode base that has been cut or severed to expose a portion of the heat dissipating core, such that the electrode tip is formed directly on the heat dissipating core using additive manufacturing.

FIELD

The present invention generally relates to spark plugs and otherignition devices and, in particular, to spark plug electrodes and othercomponents that are made using additive manufacturing processes.

BACKGROUND

Spark plugs are used to initiate combustion in internal combustionengines. Typically, spark plugs ignite an air/fuel mixture in acombustion chamber so that a spark is produced across a spark gapbetween two or more electrodes. The ignition of the air/fuel mixture bymeans of the spark triggers a combustion reaction in the combustionchamber, which is responsible for the power stroke of the engine. Thehigh temperatures, the high electrical voltages, the rapid repetition ofcombustion reactions, and the presence of corrosive materials in thecombustion gases can create a harsh environment in which the spark plugmust function. The harsh environment can contribute to an erosion and/orcorrosion of the electrodes, which can negatively affect the performanceof the spark plug over time.

To reduce erosion and/or corrosion of the electrodes, various kinds ofprecious metals and alloys have been used, such as those having platinumand iridium. These materials are expensive, however, particularlyiridium. Consequently, the manufacturers of spark plugs try to minimizethe quantity of precious metals used in an electrode. One approachinvolves using precious metals only on an electrode tip or on a sparkingsection of the electrodes, i.e. in the place where a spark jumps acrossthe spark gap, as opposed to the entire electrode body itself.

Various joining techniques, such as circumferential laser welding, havebeen used for attaching a precious metal electrode tip to an electrodebody. However, when a precious metal electrode tip is circumferentiallylaser welded to an electrode body, such as a body made from a nickelalloy, there can be a substantial amount of thermal and/or otherstresses on the weld joint during operation of the spark plug due to thedifferent properties of the materials (e.g., different coefficients ofthermal expansion, different melting temperatures, etc.). Incircumferential laser welding processes where the workpiece rotates andthe laser remains fixed in a generally radial orientation, factors suchas the concentricity and uneven wear of the workpiece holder can resultin an uneven circumferential weld (e.g., the geometry and/or alloycomposition of the weld can vary around the circumference of theworkpiece), which can further exasperate the stresses mentioned above.These stresses, in turn, can undesirably lead to cracking or otherdamage to the electrode body, the electrode tip, the joint connectingthe two components, or a combination thereof.

Another challenge pertains to cooling the precious metal electrode tip.If the precious metal electrode tip is not adequately cooled and asubstantial amount of heat is allowed to build up, stresses like thosementioned above, can become even greater. This is particularly true inapplications, such as start-stop engines, that have a high frequency ofload changes coupled with high combustion temperatures in the engine.One approach to this challenge involves simply moving the thermallyconductive core closer to the precious metal electrode tip and using acircumferential laser weld to attach the electrode tip to the electrodebody, but this can create challenges of its own. One of which involves achange in the sparkover or sparking location of the electrode. It ispreferable for the sparkover location to be on the precious metalelectrode tip, as the precious metal typically provides the highestresistance to erosion and/or corrosion. However, when an electrode tipis circumferentially laser welded to an electrode base with a thermallyconductive core located near the electrode tip, the welding process candraw or pull the thermally conductive core material to the outside ofthe electrode base in the area of the weld. This, in turn, canundesirably change or shift the sparkover location from the preciousmetal electrode tip surface, where it should be, to the weld surface,which is less robust in terms of resisting erosion and/or corrosion.This change in sparkover location can have a negative impact on theservice life of the spark plug.

The spark plug electrode described herein is designed to address one ormore of the drawbacks and challenges mentioned above.

SUMMARY

According to one embodiment, there is provided a spark plug electrode,comprising: an electrode base; a heat dissipating core that is at leastpartially surrounded by the electrode base; an electrode tip that isformed on the electrode base and includes a plurality of laserdeposition layers; and a thermal coupling zone that is at leastpartially located between the electrode tip and the heat dissipatingcore, wherein the thermal coupling zone directly thermally couples theelectrode tip to the heat dissipating core.

In accordance with various embodiments, the spark plug electrode mayhave any one or more of the following features, either singly or in anytechnically feasible combination:

-   wherein the heat dissipating core extends along a center axis of the    spark plug electrode and terminates at an axial end that does not    reach an axial end of the electrode base, an axial spacing Z between    the axial end of the heat dissipating core and the axial end of the    electrode base is less than or equal to 1.3 mm;-   the heat dissipating core extends along a center axis of the spark    plug electrode and terminates at an axial end that reaches an axial    end of the electrode base, an axial spacing Z between the axial end    of the heat dissipating core and the axial end of the electrode base    is approximately 0.0 mm;-   the heat dissipating core extends along a center axis of the spark    plug electrode and terminates at an imaginary axial end that would    extend beyond an axial end of the electrode base if the imaginary    axial end had not been truncated, an axial spacing Z between the    imaginary axial end of the heat dissipating core and the axial end    of the electrode base is less than 0.0 mm;-   the spark plug electrode is a center electrode and the electrode tip    is a cylindrical component that is formed on an axial end of the    electrode base, the electrode tip is oriented such that the    plurality of laser deposition layers are perpendicular to a center    axis of the spark plug electrode, and the electrode tip is secured    to the electrode base with a weldless joint;-   the spark plug electrode is a ground electrode and the electrode tip    is a flat component that is formed on a side surface of the    electrode base, the electrode tip is oriented such that the    plurality of laser deposition layers are parallel to a center axis    of the ground electrode in an area of the electrode tip, and the    electrode tip is secured to the electrode base with a weldless    joint;-   the plurality of laser deposition layers are formed on the electrode    base by an additive manufacturing process, which uses a powder bed    fusion technique to melt or sinter precious metal-based powder onto    the electrode base with a laser or electron beam, and then to allow    the melted or sintered powder to solidify to become the laser    deposition layers of the electrode tip, the plurality of laser    deposition layers have an average layer thickness T that is between    5 μm and 60 μm, inclusive, and a total thickness of the plurality of    laser deposition layers is an electrode tip height H that is between    0.05 mm and 3.0 mm, inclusive;-   the electrode tip includes a precious metal-based material that has    at least one precious metal selected from the group consisting of:    iridium, platinum, ruthenium, palladium or rhodium;-   the precious metal-based material is either a platinum-based    material, a ruthenium-based material, or an iridium-based material    that includes no more than 60 wt % iridium;-   the electrode base includes a nickel-based material, the heat    dissipating core includes a copper-based material, and the thermal    coupling zone includes nickel from the nickel-based material, copper    from the copper-based material and precious metal from the precious    metal-based material;-   the thermal coupling zone creates a thermal conduit from the    electrode tip to the heat dissipating core that is in an interior of    the spark plug electrode such that the thermal coupling zone is not    exposed on an exterior surface of the spark plug electrode;-   the thermal coupling zone, in the location between the electrode tip    and the heat dissipating core, has a higher average thermal    conductivity than the electrode base;-   the thermal coupling zone includes a thermal coupling zone alloy    with copper from the heat dissipating core, nickel from the    electrode base, and at least one of iridium, ruthenium, or platinum    from the electrode tip;-   the thermal coupling zone includes a first portion that is located    adjacent to the heat dissipating core and a second portion that is    located adjacent to the electrode tip, the first portion includes a    thermal coupling zone alloy having 2-45 wt % of a precious metal    from the electrode tip, and the second portion includes a thermal    coupling zone alloy having 2-45 wt % of copper from the heat    dissipating core;-   a proportion of the precious metal in the thermal coupling zone    alloy decreases along a center axis from the second portion to the    first portion, and a proportion of the copper in the thermal    coupling zone alloy decreases along the center axis from the first    portion to the second portion to create a composition gradient    structure;-   the thermal coupling zone includes a first portion that is located    adjacent to the heat dissipating core and a second portion that is    located adjacent to the electrode tip, the first portion has a    bulbous shape and absorbs an axial end of the heat dissipating core,    the second portion has a wide and shallow shape and fills in an area    underneath the electrode tip; and-   the electrode tip is built on a severed end of an electrode body    that has an exposed surface of the heat dissipating core so that a    truncated axial end of the heat dissipating core is absorbed into    the thermal coupling zone.

According to another embodiment, there is provided a spark plugelectrode, comprising: an electrode base including a nickel-basedmaterial; a heat dissipating core including a copper-based material, theheat dissipating core is at least partially surrounded by the electrodebase; an electrode tip including a precious metal-based material, theelectrode tip is formed on the electrode base with an additivemanufacturing process and includes a plurality of laser depositionlayers that are perpendicular to a center axis of the spark plugelectrode; and a thermal coupling zone that is at least partiallylocated between the electrode tip and the heat dissipating core, thethermal coupling zone creates a thermal conduit from the electrode tipto the heat dissipating core that is in an interior of the spark plugelectrode such that the thermal coupling zone is not exposed on anexterior surface of the spark plug electrode, and the thermal couplingzone includes nickel from the nickel-based material, copper from thecopper-based material and precious metal from the precious metal-basedmaterial, wherein the thermal coupling zone directly thermally couplesthe electrode tip to the heat dissipating core.

According to yet another embodiment, there is provided an additivemanufacturing process for manufacturing a spark plug electrode,comprising the steps of: providing an electrode body that includes anelectrode base and a heat dissipating core that is at least partiallysurrounded by the electrode base; covering a firing end of the electrodebody with a thin powder bed layer that includes a precious metal-basedmaterial; directing a laser or an electron beam at the firing end of theelectrode body such that it melts or sinters at least some of the thinpowder bed layer; repeating the covering and directing steps for aplurality of cycles so that an electrode tip with a plurality of laserdeposition layers is formed on the electrode base and so that a thermalcoupling zone is formed at least partially between the electrode tip andthe heat dissipating core, wherein the thermal coupling zone directlythermally couples the electrode tip to the heat dissipating core.

In accordance with various embodiments, the additive manufacturingprocess may have any one or more of the following features, eithersingly or in any technically feasible combination:

-   the providing step further includes providing the electrode body    with the electrode base being severed or cut through the heat    dissipating core so that a portion of the heat dissipating core is    exposed at an axial end;-   the directing step further includes directing the laser or the    electron beam at the firing end of the electrode body and driving    the laser or the electron beam according to a non-uniform energy    profile that concentrates more energy towards a center of the firing    end and less energy towards a radially outer section of the firing    end;-   the non-uniform energy profile drives the laser or the electron beam    with a higher energy level when it melts or sinters the thin powder    bed layer in a circular zone located towards the center of the    firing end, and the non-uniform energy profile drives the laser or    the electron beam with a lower energy level when it melts or sinters    the thin powder bed layer in an annular zone that is concentric with    the circular zone and is located towards the radially outer section    of the firing end; and-   the non-uniform energy profile helps create a customized thermal    coupling zone that includes a first portion that is located deeper    in the electrode body and is concentrated towards a center of the    electrode body, and a second portion that is located closer to the    electrode tip and is more spread out so that it is largely    underneath the electrode tip.

DRAWINGS

Preferred embodiments will hereinafter be described in conjunction withthe appended drawings, wherein like designations denote like elements,and wherein:

FIG. 1 is a side view of a spark plug;

FIG. 2 is a cross-sectional view of a firing end of the spark plug inFIG. 1 , where the firing end has an electrode tip that is built onto anelectrode base via an additive manufacturing process such that it isdirectly thermally coupled to a heat dissipating core;

FIGS. 3-4 are cross-sectional views of other examples of firing ends ofspark plugs, where the firing ends have electrode tips that are builtonto electrode bases via additive manufacturing processes such that theyare directly thermally coupled to heat dissipating cores;

FIGS. 5-7 are cross-sectional views of electrodes that may be used withthe various spark plug examples shown in FIGS. 1-4 , where each of theelectrodes has a precious metal-based electrode tip that is formed byadditive manufacturing and is directly thermally coupled to a heatdissipating core;

FIG. 8 is a flowchart of an additive manufacturing process that may beused with the various spark plug examples shown in FIGS. 1-4 or theelectrode examples shown in FIGS. 5-7 to form a precious metal-basedelectrode tip that is directly thermally coupled to a heat dissipatingcore; and

FIGS. 9, 10A, 11A and 12A are cross-sectional views and FIGS. 10B, 11Band 12B are end views of electrodes at different stages of manufacturingthat coincide with the additive manufacturing process of FIG. 8 .

DESCRIPTION

The spark plug electrode disclosed herein includes an electrode tip thatis formed on an electrode base using an additive manufacturing process,such as a powder bed fusion technique, such that the electrode tip isdirectly thermally coupled to a heat dissipating core. Some non-limitingexamples of potential powder bed fusion techniques that may be usedinclude: selective laser melting (SLM), selective laser sintering (SLS),direct metal laser sintering (DMLS), and electron beam melting (EBM).

By way of example, the electrode base may be made of a nickel-basedmaterial and can surround a heat dissipating core made of a copper-basedmaterial, while the electrode tip is made of a precious metal-basedmaterial, such as one having iridium, platinum, palladium, ruthenium,rhodium, etc. The precious metal-based material is selected to improvethe resistance of the spark plug electrode to corrosion and/orelectrical erosion. By using an additive manufacturing process todirectly build the electrode tip on the electrode base, a spark plugelectrode with desirable cooling properties can be formed where theelectrode tip is directly thermally coupled to the heat dissipatingcore. Those skilled in the art will appreciate that when a preciousmetal-based electrode tip is joined to a nickel-based electrode base,such as by circumferential laser welding, there is typically asubstantial amount of thermal and/or other stresses on the weld jointduring operation of the spark plug due to various factors (e.g.,different coefficients of thermal expansion, different meltingtemperatures, uneven or nonuniform circumferential welds, etc.). Thesestresses, in turn, can undesirably lead to cracking or other damage tothe electrode base, the electrode tip, the joint connecting the twocomponents, or a combination thereof. There is also the possibility thatwhen a circumferential laser weld is used to attach a preciousmetal-based electrode tip to an electrode base, the laser weldingprocess can draw or pull the copper-based material of the heatdissipating core to the circumferential sides of the electrode. This canhave the undesirable result of creating a sparkover location on thecircumferential side of the electrode, away from the intended sparkingsurface, which in turn reduces the service life of the spark plug. Theseand other challenges are exacerbated in internal combustion engines,like start-stop engines, where a spark plug electrode is subjected toharsh conditions and extreme temperature and/or load changes. The sparkplug electrode described herein, with an electrode tip formed byadditive manufacturing so that it is directly thermally coupled to aheat dissipating core, is designed to address such challenges in aneconomical manner.

The spark plug electrode disclosed herein may be used in a wide varietyof spark plugs and other ignition devices including industrial sparkplugs, automotive spark plugs, aviation igniters, glow plugs, prechamberplugs, or any other device that is used to ignite an air/fuel mixture inan engine or other piece of machinery. This includes, but is certainlynot limited to, the exemplary industrial spark plugs that are shown inthe drawings and are described below. Furthermore, it should be notedthat the present spark plug electrode may be used as a center and/orground electrode. Other embodiments and applications of the spark plugelectrode are also possible. Unless otherwise specified, all percentagesprovided herein are in terms of weight percentage (wt %) and allreferences to axial, radial and circumferential directions are based onthe center axis A of the spark plug or spark plug electrode.

Referring to FIGS. 1 and 2 , there is shown an exemplary spark plug 10that includes a center electrode 12, an insulator 14, a metallic shell16, and a ground electrode 18. The center electrode 12 is disposedwithin an axial bore of the insulator 14 and includes a firing end 20that protrudes beyond a free end 22 of the insulator 14. As explainedbelow in more detail, the firing end 20 may include an electrode base 30made from a nickel-based material, a heat dissipating core 32 that isencompassed within the electrode base and is made from a copper-basedmaterial, and an electrode tip 34 made from a precious metal-basedmaterial, where the electrode tip is formed on the electrode base usingan additive manufacturing process so that the electrode tip is directlythermally coupled to the heat dissipating core. Insulator 14 is disposedwithin an axial bore of the metallic shell 16 and is constructed from amaterial, such as a ceramic material, that is sufficient to electricallyinsulate the center electrode 12 from the metallic shell 16. The freeend 22 of the insulator 14 may be retracted within a free end 24 of themetallic shell 16, as shown, or it may protrude beyond the metallicshell 16. The ground electrode 18 may be constructed according to theconventional J-gap configuration shown in some of the drawings oraccording to some other arrangement, and is attached to the free end 24of the metallic shell 16. According to this particular embodiment, theground electrode 18 includes a side surface 26 that opposes the firingend 20 of the center electrode and has an electrode tip or piece 40 thatmay or may not be formed according to the additive manufacturing processdescribed herein, as well as a heat dissipating core 42 of its own. Theelectrode tip 40 is in the form of a flat pad and defines a spark gap Gwith the electrode tip 34 of the center electrode such that they providesparking surfaces for the emission, reception, and exchange of electronsacross the spark gap G. The electrode tips 34 and 40 may be formed fromthe same precious metal-based material or they may be formed fromdifferent precious metal-based materials.

In the example shown in FIGS. 1 and 2 , the electrode base 30 is anextension of and is made from the same nickel-based material as a mainelectrode body 36. The electrode base 30 is part of the electrode body36 and may have the same diameter (as shown), or it may be machined,drawn down, or otherwise manufactured so that it has a smaller diameterthan that of the adjacent electrode body 36 and, thus, provides apedestal or surface upon which the electrode tip 34 can be built. Aswill be explained more thoroughly, an additive manufacturing process maybe used to form the electrode tip 34 directly on the electrode base 30by selectively directing a laser or electron beam at a bed of preciousmetal-based powder that is brought into contact with an axial end of theelectrode base. This causes the precious metal-based powder, as well asportions of the electrode base 30 and/or the heat dissipating core 32,to melt or intermix together and solidify at the firing end 20. Theadditive manufacturing process is then repeated so that the preciousmetal-based electrode tip 34 is built up, one layer at a time, on theelectrode base 30 until it reaches its desired height. By controllingvarious parameters, such as a laser energy distribution and an axialspacing between an axial end of the heat dissipating core and an axialend of the electrode base, the additive manufacturing process is able toestablish a direct thermal coupling or connection between the electrodetip and the heat dissipating core that can have a significant impact onthe thermal management of the electrode.

As mentioned above, the present spark plug electrode is not limited tothe exemplary configuration shown in FIGS. 1 and 2 , as it may beemployed in any number of different applications, including variousindustrial spark plugs, automotive spark plugs, aviation igniters, glowplugs, prechamber plugs, or other devices. The present spark plugelectrode is also not limited to center electrodes, as it may be aground or earth electrode of some type. Some non-limiting examples ofother potential applications where the present spark plug electrodecould be used are illustrated in FIGS. 3 and 4 , where similar referencenumerals as FIGS. 1 and 2 denote similar features. Numerous otherembodiments and examples, such as various types of plugs with differentaxial, radial and/or semi-creeping spark gaps; prechamber,non-prechamber, shielded and/or non-shielded configurations; multiplecenter and/or ground electrodes; as well as plugs that burn or ignitegasoline, diesel, natural gas, hydrogen, propane, butane, etc. arecertainly possible. The spark plug electrode and method of the presentapplication are in no way limited to the illustrative examples shown anddescribed herein.

In FIG. 3 , the spark plug has a ground electrode 18′ with a bridge-typedesign, as opposed to a J-gap design, that is attached to the free end24′ of the metallic shell 16′ at several locations. The center electrode12′ is at least partially surrounded by an insulator 14′ and includes anelectrode base 30′ towards its firing end 20′ that has the same diameteras an adjacent electrode body 36′ (this is not required, as theelectrode base 30′ could have a different diameter, it could be tapered,it could be stepped, etc. to cite several possibilities). Like theprevious example, an electrode tip 34′ is built or formed onto theelectrode base 30′ using an additive manufacturing process and a bed ofprecious metal-based powder. This process forms a thermal coupling zone38′ that may be at least partially located between a heat dissipatingcore 32′ and the electrode tip 34′ and thermally connects or links thetwo components in a more substantial way than if the electrode tip wassimply circumferentially laser welded onto the electrode base. Thedrawings show the end of the heat dissipating core 32′ being morerounded or blunted in shape and the thermal coupling zone 38′ beingflatter than their counterparts in FIG. 2 . It should be appreciatedthat the size, shape, location, orientation and/or composition of theheat dissipating core, the thermal coupling zone and/or the electrodetip may vary depending on the specific application in which they areused and such components are not limited to the illustrative examplesshown herein. An electrode tip or piece 40′, which is optional and ispreferably made of a precious metal-based material, can be formed by thepresent additive manufacturing process or it can be welded onto a sidesurface 26′ of the bridge ground electrode 18′ to define a spark gap Gwith the electrode tip 34′. The electrode tips 34′ and 40′ may be formedfrom the same precious metal-based material or they may be formed fromdifferent precious metal-based materials. Other embodiments are possibleas well.

Turning to FIG. 4 , the spark plug is a prechamber plug with a centerelectrode 12″, an insulator 14″, a metallic shell 16″ and a groundelectrode 18″. The center electrode 12″ includes an electrode base 30″with a precious metal-based electrode tip 34″ formed thereon, a heatdissipating core 32″ and an electrode body 36″, and the center electrodeextends into a prechamber space or volume 46″. A radial spark gap G isformed between an outer circumferential surface of the center electrodetip 34″ and an inner circumferential surface of a ring-shaped electrodepiece 40″ that is held in place by several ground electrodes or groundelectrode holders 18″. The additive manufacturing process describedherein may be used to form the precious metal-based electrode tip 34″ onthe axial end of the electrode base 30″, one layer at a time, so thatthe electrode tip 34″ becomes directly thermally coupled to the heatdissipating core 32″ via a thermal coupling zone 38″. In this example,the ring-shaped electrode piece 40″ is made of a precious metal-basedmaterial and is attached to the ground electrodes 18″ via welding or thepresent additive manufacturing process. The electrode tips and pieces34″ and 40″ may be formed from the same precious metal-based material orthey may be formed from different precious metal-based materials.

Turning now to FIGS. 5-7 , there are shown several enlarged schematicillustrations of center electrode firing ends, such as ones that couldbe used with the plugs in FIGS. 1-4 . In each case, a center electrode12, 12′, 12″ has a firing end 20, 20′, 20″ that includes an electrodebase 30, 30′, 30″, a heat dissipating core 32, 32′, 32″, an electrodetip 34, 34′, 34″, and a thermal coupling zone 38, 38′, 38″ that acts asa thermal conduit between the electrode tip and the heat dissipatingcore such that the two components are directly thermally coupled to oneanother. Increasing the thermal communication between the electrode tip34, 34′, 34″ and the heat dissipating core 32, 32, 32″ enables theelectrode tip to cool off more effectively during operation which, inturn, allows for a wider range of precious metal-based materials to beused in the electrode tip, including materials that are more costeffective. To explain, the electrical erosion rate and hence, theeffective service life, of an electrode tip is impacted by severalfactors, including the melting point of the precious metal-basedmaterial. Iridium, with a melting point of about 2450° C., has a greaterresistance to electrical erosion than platinum, with a melting point ofabout 1750° C. Electrode tips made from iridium-based materialstypically display a more robust resistance to electrical erosion thanthose made from platinum-based materials and, thus, are sometimes moresought after. However, iridium can cost more, and in some instances,substantially more than platinum, so it may be desirable to minimize theamount of iridium and/or other high-cost materials in the production ofthe electrode tip. The present spark plug electrode accomplishes this byusing additive manufacturing techniques to form an electrode tip 34,34′, 34″ on an electrode base 30, 30′, 30″ such that the electrode tipis directly thermally coupled to a heat dissipating core 32, 32′, 32″via a thermal coupling zone 38, 38′, 38″, which keeps the electrode tipcooler and enables the use of a wider array of precious metal-basedmaterials, including less expensive materials with lower melting points.It should be appreciated that the following descriptions of theelectrode base, the electrode tip, the heat dissipating core and thethermal coupling zone are not limited to the center electrodes shown inthe drawings and are also applicable to other center electrode and/orground electrode embodiments. For instance, a ground electrode having anelectrode base made from a nickel-based material, an electrode tip madefrom a precious metal-based material, and a heat dissipating core(whether it be a single-material core or a multi-material core) madefrom one or more thermally conductive materials could be providedaccording to the present application. In such an arrangement, theelectrode tip may be formed, using the present additive manufacturingtechniques, on a side surface or an axial end surface of the electrodebase such that the electrode tip is directly thermally coupled to theheat dissipating core, as explained. This and other center and/or groundelectrode embodiments are certainly within the scope of the presentapplication.

Electrode base 30, 30′, 30″ is typically the section or portion of theelectrode on which the electrode tip is formed by additive manufacturingand, thus, can act as a carrier material for the electrode tip. Asmentioned above, the electrode base 30, 30′, 30″ may be an integralextension of an electrode body 36, 36′, 36″ or it may be a separatepiece or component that is welded, additive manufactured, or otherwiseattached to the electrode body. The electrode base 30, 30′, 30″ can bemanufactured by drawing, extruding, machining, and/or using some otherconventional process and may be made from a nickel-based material. Theterm “nickel-based material,” as used herein, means a material in whichnickel is the single largest constituent of the material by weight, andit may or may not contain other constituents (e.g., a nickel-basedmaterial can be pure nickel, nickel with some impurities, or anickel-based alloy). According to one example, the electrode base 30,30′, 30″ is made from a nickel-based material having a relatively highweight percentage of nickel, such as a nickel-based material comprising98 wt % or more nickel. In a different example, the electrode base 30,30′, 30″ is made from a nickel-based material having a lower weightpercentage of nickel, like a nickel-based material comprising 50-90 wt %nickel (e.g., INCONEL™ 600 or 601). One particularly suitablenickel-based material has about 70-80 wt % nickel, 10-20 wt % chromium,5-10 wt % iron, as well as other elements in smaller quantities. Fornickel-based materials, the electrode base 30, 30′, 30″ may have acoefficient of thermal expansion between 10×10⁻⁶ m/mK and 15×10⁻⁶ m/mK(measured at 100° C.), a melting temperature between 1,200° C. and1,600° C., and a thermal conductivity between 10 W/m·K and 20 W/m·K(measured at 100° C.). The diameter or size of the electrode base 30,30′, 30″ can vary substantially depending on the particular applicationand embodiment (e.g., the size of electrode base 30, which is part ofthe center electrode, is likely smaller than that of an electrode basefor electrode tip 40, which is part of the ground electrode; also thesize of an electrode base for an industrial plug is likely larger thanthat of one for an automotive plug). According to the non-limitingexamples shown in FIGS. 2-4 , which are industrial plugs, the electrodebase may have a diameter between 1.4 mm and 4.2 mm, inclusive, and evenmore preferably between 1.8 mm and 3.8 mm, inclusive. For automotive andother plugs, these dimensions may be smaller and the electrode base mayhave a diameter between 0.7 mm and 3.0 mm, inclusive, and even morepreferably between 1.0 mm and 2.5 mm, inclusive. Other materials,including those that are not nickel-based, and other sizes and shapesmay be used for the electrode base 30, 30′, 30″ instead (e.g., theelectrode base does not have to include a circular cross-section with a“diameter,” but instead could include an oval, square, rectangular orother cross-section with a “dimension”).

Heat dissipating core 32, 32′, 32″ is a section or portion of theelectrode, usually an elongated portion extending along a center axis,that is at least partially encompassed or surrounded by the electrodebase and is designed to convey heat or thermal energy away from thefiring end. The exact size, shape and location of the heat dissipatingcore 32, 32′, 32″ can vary by application, but typically it is anelongated interior portion that extends along the center axis of theelectrode and is circumferentially surrounded by the nickel-basedmaterial of the electrode base so that it is not exposed on the sides ofthe electrode. In the illustrated example of FIG. 5 , the heatdissipating core 32 has elongated sides 50, 52 that extend in thelengthwise direction of the core, tapered sides 54, 56 that convergetowards an end of the core, and an axial end 58 where the coreterminates. The heat dissipating core 32 is made from one or morethermally conductive materials, such as copper- or silver-basedmaterials, having a greater thermal conductivity than that of thesurrounding electrode base 30. The thermally conductive material mayhave a thermal conductivity greater than 70 W/m·K (measured at 100° C.)and, even more preferably, a thermal conductivity greater than 200 W/m·K(measured at 100° C.). The term “copper-based material,” as used herein,means a material in which copper is the single largest constituent ofthe material by weight, and it may or may not contain other constituents(e.g., a copper-based material can be pure copper, copper with someimpurities, or a copper-based alloy). According to one example, the heatdissipating core 32, 32′, 32″ is made from a thermally conductivematerial that is a copper-based material having a relatively high weightpercentage of copper, such as a copper-based material comprising 90 wt %or more copper. For copper-based materials, the heat dissipating core32, 32′, 32″ may have a coefficient of thermal expansion between 14×10⁻⁶m/mK and 19×10⁻⁶ m/mK (measured at 100° C.), a melting temperaturebetween 950° C. and 1,200° C., and a thermal conductivity greater than275 W/m·K (measured at 100° C.).

The elongated sides 50, 52 are generally parallel to one another and thecenter axis A and help form the outer boundary of the heat dissipatingcore 32. As mentioned above, it is typically undesirable for the heatdissipating core material, which is much less resistant to corrosionand/or erosion than the precious metal-based material and is highlyconductive, to be exposed on the outer surface of the electrode where itcan become an unintended sparkover location. Thus, it is preferable thatthe heat dissipating core 32, in the area of the elongated sides 50, 52,be covered with a sheath or casing of the electrode base 30 having aradial thickness X on each side that is greater than or equal to 0.2 mm.

The heat dissipating core 32 typically does not terminate in a perfectlysquared off form, but rather gradually narrows or tapers towards theaxial end 58. This can be due to design factors or to the manufacturingprocess, such as when the heat dissipating core is initially insertedinto an electrode base cup and is then co-extruded or co-drawn with theelectrode base. In some examples, the tapered sides 54, 56 are generallystraight, angled segments that gradually converge towards one another(e.g., as shown in FIG. 2 ), but it is also possible for the taperedsides to be rounded (e.g., as shown in FIG. 3 ) or even more squared off(e.g., as shown in FIG. 4 ). It is preferable, although not required,that a radial thickness Y of the electrode base material 30 in the areaof the tapered sides 54, 56 (as measured approximately halfway betweenthe axial beginning and axial end of a tapered side) be greater than orequal to 0.3 mm, but such a dimension depends greatly on the shape ofthe heat dissipating core 32 in this area.

The axial end 58 of the core can have any number of different shapes andconfigurations, including ones that are pointed, rounded, blunted,squared-off, etc. The location of the axial end 58 dictates an axialspacing Z, which is the axial distance between the axial end 58 of thecore and the axial end 60 of the electrode base, not counting theelectrode tip 34. Axial spacing Z can have a significant impact on thethermal coupling between the electrode tip 34 and the heat dissipatingcore 32 and can affect both the operation of the spark plug, as well asits manufacture. In a non-limiting example, the axial spacing Z is lessthan or equal to 1.3 mm, even more preferably is less than or equal to1.05 mm, even more preferably is less than or equal to 0.8 mm, and evenmore preferably is less than or equal to 0.55 mm. In some examples, itis even possible for the axial end 58 of the heat dissipating core 32 tobe at the same axial position as the axial end 60 of the electrode base30 (e.g., see FIG. 6 ) so that the axial spacing Z is essentially 0 mm,or for the axial end 58 of the heat dissipating core to be cut off(e.g., see FIG. 7 ) so that the axial spacing Z is a negative dimension.Testing has revealed, however, that simply decreasing and/or increasingthe axial spacing Z, if not adequately offset with other precautions,can present challenges of its own. For instance, if the axial spacing Zis too small in some conventional plugs, then it can be difficult toproduce reliable circumferential laser welds, as the close proximity ofa heat dissipating core causes it to pull substantial amounts of heataway from the welding area which, in turn, can impact the quality of theweld. If, on the other hand, the axial spacing Z is too large in certainconventional plugs, then there is insufficient thermal coupling betweenan electrode tip and a heat dissipating core, as the interposednickel-based material with its lower thermal conductivity can act as athermal barrier of sorts between the components. The present spark plugelectrode overcomes these and other challenges by using an additivemanufacturing process to form the electrode tip 34 on the electrode base30 such that they are directly thermally coupled to one another via thethermal coupling zone 38.

Although the heat dissipating core 32, 32′, 32″ is shown in the drawingsas a single-material core (i.e., a core formed from a single thermallyconductive material, which may or may not include multipleconstituents), it is also possible for it to be a multi-material core.According to a first example of a multi-material core, an inner heatdissipating core component (e.g., one made from a nickel-based material)extends along a portion of the electrode, and an outer heat dissipatingcore component (e.g., one made from a copper-based material) extendsalong the same portion of the electrode such that it at least partiallysurrounds and is concentric with the inner heat dissipating corecomponent. In this concentric or layered arrangement, it is possible forthe inner heat dissipating core component to extend or protrude beyondthe end of the outer heat dissipating core component. According to asecond example of a multi-material core, a forward heat dissipating corecomponent extends along a portion of the electrode that is closer to afiring end, and a rearward heat dissipating core component extends alonga portion of the electrode that is further from the firing end. In thisend-to-end or serial arrangement, one of the heat dissipating corecomponents may be longer than the other. The first and/or secondmulti-material core examples may be used with a center electrode and/ora ground electrode. If a multi-material core is used, the axial spacingZ is measured from the axial end of the closest heat dissipating corecomponent to the electrode tip (i.e., the shortest axial spacing Z). Ofcourse, numerous other heat dissipating core arrangements andconfigurations are possible and are certainly within the scope of thepresent application.

Electrode tip 34, 34′, 34″ is the section or portion of the electrode,usually the sparking portion, that is typically formed on the electrodebase by additive manufacturing. As such, the electrode tip 34, 34′, 34″may be made from a bed of precious metal-based powder that is broughtinto close proximity with the electrode base so that, when irradiated bya laser or electron beam, the precious metal-based powder and some ofthe solid material of the electrode base 30 and/or the heat dissipatingcore 32 are melted and solidify into laser deposition layers. Thisprocess of creating individual layers is repeated, thereby creating anumber of laser deposition layers 70 that are sequentially built orstacked on one another such that the layers are perpendicular to thecenter axis A of the electrode (being “perpendicular” in this contextdoes not require perfect perpendicularity, so long as layers 70 are,when viewed in cross-section, perpendicular to center axis A within atolerable margin of error). Some of the laser deposition layers 70 mayhave materials from the heat dissipating core 32, the electrode base 30and the electrode tip 34; some layers 70 may only have material from theelectrode base 30 and the electrode tip 34; while other layers 70 mayonly have material from the electrode tip 34. Each laser depositionlayer has an average layer thickness T, which may be between 5 μm and 60μm, and the total or sum of all of the layer thicknesses is theelectrode tip height H, which may be between 0.05 and 3.0 mm, or evenmore preferably between 0.1 and 1.5 mm. The electrode tip 34, 34′, 34″may be produced according to embodiments that: are diametrically reducedwith respect to an electrode base, as well as those that are not; are inthe shape of rivets, cylinders, bars, columns, wires, balls, mounds,cones, flat pads, disks, plates, rings, sleeves, etc.; are circular,oval, square, rectangular and/or other shaped, in terms of itscross-section; are located at an axial end of an electrode base, as wellas those that are located on a side surface or other part of theelectrode base; and are part of a center electrode or a groundelectrode, to cited a few possibilities.

The electrode tip 34, 34′, 34″ may be made from a precious metal-basedmaterial so as to provide improved resistance to corrosion and/orerosion. The term “precious metal-based material,” as used herein, meansa material in which a precious metal is the single largest constituentof the material by weight, and it may or may not contain otherconstituents (e.g., a precious metal-based material can be pure preciousmetal, precious metal with some impurities, or a precious metal-basedalloy). Precious metal-based materials that may be used includeiridium-, platinum-, ruthenium- palladium- and/or rhodium-basedmaterials, to cite a few possibilities. According to one example, theelectrode tip 34, 34′, 34″ is made from an iridium-, platinum- orruthenium-based material, where the material has been processed into apowder form so that it can be used in the additive manufacturingprocess. For iridium-based materials, the electrode tip may have acoefficient of thermal expansion between 6×10⁻⁶ m/mK and 7×10⁻⁶ m/mK(measured at 100° C.), a melting temperature between 2,300° C. and2,500° C., and a thermal conductivity between 120 W/m·K and 180 W/m·K(measured at 100° C.); for platinum-based materials, the electrode tipmay have a coefficient of thermal expansion of between 8×10⁻⁶ m/mK and10×10⁻⁶ m/mK (measured at 100° C.), a melting temperature between 1,650°C. and 1,850° C., and a thermal conductivity between 50 W/m·K and 90W/m·K (measured at 100° C.). As mentioned above, certain preciousmetals, like iridium, can be very expensive, thus, it is typicallydesirable to reduce the content of such materials in the electrode tip,so long as doing so does not unacceptably degrade the performance of theelectrode tip. Precious metal-based powders with no more than 60 wt %iridium (e.g., Pt—Ir40, Pt—Ir50, Ir—Pt40, Ru—Rh5, etc.), and preferablywith no more than 50 wt % iridium (e.g., Pt—Ir40, Pt—Ir50, Ru—Rh5,etc.), can be used to make the electrode tip 34, 34′, 34″ when the tipis directly thermally coupled to the heat dissipating core 32, 32′, 32″,as such materials can strike a desirable balance between cost andperformance. However, other precious-metal based powders, such as thosewith up to about 98 wt % iridium (e.g., Ir—Rh2.5, Ir—Rh5, Ir—Rh10,Ir—Pt5, Ir—Pt5-Rh5), etc.), may be used as well, particularly if theprices of such materials come down in the future. The diameter or sizeof the electrode tip 34, 34′, 34″ varies depending on the particularapplication and embodiment. For instance, in the non-limiting examplesshown in FIGS. 2-4 , which are industrial plugs, each of the electrodetips may have a diameter between 1.0 mm and 4.2 mm, inclusive, and evenmore preferably between 1.2 mm and 3.0 mm, inclusive. For automotive andother plugs, these dimensions will likely be smaller and the electrodetip may have a diameter between 0.4 mm and 3.0 mm, inclusive, and evenmore preferably between 0.6 mm and 2.0 mm, inclusive. The electrode tipdoes not have to include a circular cross-section with a “diameter,” butinstead could include an oval, square, rectangular or othercross-section with a “dimension.”

Thermal coupling zone 38, 38′, 38″ is located at least partially betweenthe heat dissipating core and the electrode tip and includes materialfrom the heat dissipating core, the electrode base and/or the electrodetip. The thermal coupling zone 38, 38′, 38″ is designed to act as athermal conduit or channel so that heat that builds up during operationof the spark plug can be effectively conveyed or transferred away fromthe electrode tip 34, 34′, 34″ to the heat dissipating core 32, 32′,32″, from which point it can further dissipate into the insulator 14,the shell 16 and eventually the cylinder head of the engine. Asexplained above, increased cooling of the electrode tip 34, 34′, 34″ isdesirable for a number of reasons: it reduces the thermal stresses thatarise at the junction between the electrode tip and electrode base; itdecreases the rate of erosion and/or corrosion of the electrode tip; andit enables the use of a wider variety of precious metal-based materials,including less expensive materials with lower melting points, as well asless precious metal material, to name but a few. The thermal couplingzone 38, 38′, 38″ is located in the interior of the electrode so thatits concentrated towards the center or middle of the electrode, and itmay include material from the heat dissipating core 32, 32′, 32″, theelectrode base 30, 30′, 30″ and/or the electrode tip 34, 34′, 34″ (whenthey are all present in the thermal coupling zone, these materialstogether make a thermal coupling zone alloy). By containing the thermalcoupling zone 38, 38′, 38″ in the middle of the electrode, it preventsit from being exposed on an exterior and becoming an unwanted sparkoverlocation. Furthermore, the thermal coupling zone alloy has a higheraverage thermal conductivity than that of the electrode base 30, 30′,30″ by itself, which can sometimes act like a thermal barrier orimpediment in plugs where a substantial amount of electrode basematerial is interposed between the tip and core. The combination of thethermal coupling zone alloy (e.g., Ni—Ir—Cu, Ni—Pt—Cu, Ni—Ir—Pt—Cu,etc.), the close proximately between the electrode tip and the heatdissipating core (e.g., less than 2.0 mm), and the concentrated shape ofthe thermal coupling zone (e.g., a somewhat elongated shape along thecenter axis A of the electrode) helps create a direct thermal couplingor connection between the electrode tip and the heat dissipating core,without undesirably creating an unwanted sparkover point on the side ofthe electrode. The thermal coupling zone 38, 38′, 38″ also helps reducestresses, such as those caused by different rates of thermal expansion,at the junction between the electrode tip and base. The followingparagraphs describe different examples of thermal coupling zones and areprovided in conjunction with FIGS. 5-7 . It should be appreciated thatthese drawings are only schematic illustrations, as the heat dissipatingcores, the thermal coupling zones, the electrode bases, the electrodetips, etc. may appear differently than those illustrated.

In FIG. 5 , there is shown an example of a thermal coupling zone 38 thatmay be used with the spark plug of FIG. 2 . Since the axial end 58 ofthe heat dissipating core 32 does not reach the axial end 60 of theelectrode base 30, the electrode 12 has an axial spacing Z that isapproximately 0.5 mm. The distribution or concentration of materials inthe thermal coupling zone 38 may vary along the center axis A, butelements from the heat dissipating core 32, the electrode base 30, andthe electrode tip 34 are all present in the thermal coupling zone 38.Preliminary tests suggest that in a first portion 80 of the thermalcoupling zone 38, which is adjacent the heat dissipating core 32 and isfurthest from the electrode tip 34, the thermal coupling zone mayinclude a thermal coupling zone alloy having approximately: 2-45 wt % ofa precious metal (e.g., Ir, Pt, Pd, Ru, Rh, etc.), 2-50 wt % of copper,20-75 wt % of nickel, and the remainder being other elements from theelectrode components. In a second portion 82 of the thermal couplingzone that is adjacent the electrode tip 34 and is furthest from heatdissipating core 32, the thermal coupling zone may include a thermalcoupling zone alloy having approximately: 10-65 wt % of a precious metal(e.g., Ir, Pt, Pd, Ru, Rh, etc.), 2-45 wt % of copper, 10-65 wt % ofnickel, and the remainder being other elements from the electrodecomponents. Even though the exact composition of the thermal couplingzone 38 may vary from the examples provided above, it is preferable thata thermal coupling zone alloy include thermally conductive material fromthe heat dissipating core 32, nickel from the electrode base 30, andprecious metal from the electrode tip 34 and that the thermal couplingzone be configured according to a gradient structure so that the firstportion 80 has a greater amount of copper than the second portion 82,and that the second portion 82 has a greater amount of precious metalthan the first portion 80.

FIG. 6 shows another possible example of a thermal coupling zone 38′which may be used with the spark plug of FIG. 3 . In this example, theaxial end 58′ of the heat dissipating core 32′ reaches the axial end 60′of the electrode base 30′ so that electrode 12′ has an axial spacing Zthat is approximately 0.0 mm. As illustrated, the electrode body 36′ hasbeen cut or severed such that axial end 58′ of the heat dissipating core32′ is at or is nearly at the axial end 60′ of the electrode base 30′(hence the axial spacing Z of approximately 0.0 mm). When the additivemanufacturing process begins building the initial layers of theelectrode tip 34′, a laser or electron beam is directed in the axialdirection such that it melts a thin coating of precious metal-basedpowder covering the axial end 60′, as well as melting some of theunderlying electrode base 30′ and the heat dissipating core 32′. Due tothe precise nature of additive manufacturing processes, such as thoseusing powder bed fusion techniques, a disproportional amount of energycan be concentrated or directed towards the center of the electrode,which in turn can start to create a deeper thermal coupling zone 38′ inthis area. This process may continue, layer by layer with its energyconcentration towards the center or middle of the axial end 60′, so thatthe thermal coupling zone 38′ becomes deeper towards the middle of theelectrode. It is possible, although not required, that the thermalcoupling zone 38′ could become somewhat spherical or bulbous in shapetowards the middle; this is illustrated in FIG. 6 , where the axial end58′ of the heat dissipating core 32′ has been at least partiallyabsorbed into the bulbous-shaped first portion 80′ of the thermalcoupling zone 38′. A second portion 82′ of the thermal coupling zone 38′may be wider and shallower in shape so that it fills in a majority ofthe area underneath the electrode tip 34′, but does not extend as deepinto the electrode as the first portion 80′. The thermal coupling zone38′ may have a composition and/or gradient structure similar to thatdescribed above in connection with the previous example

In FIG. 7 , there is illustrated another example of a thermal couplingzone 38″ which may be used with the spark plug in FIG. 4 . In thisexample, before the electrode tip 34″ was added, the electrode body 36″was severed at position that cut through the heat dissipating core 32″(i.e., the axial end of the heat dissipating core was cut off to exposea surface of the core). Thus, the axial spacing Z between an imaginaryaxial end 58″ (where it would have been if it had not been cut off, asindicated in broken lines) and an axial end 60″ of the electrode base30″ is a negative dimension, such as between 0.0 mm and −0.5 mm. Due tothe close axial proximately between the bulk of the heat dissipatingcore 32″ and the electrode tip 34″, this example will likely exhibithigh thermal conductivity such that the electrode tip can be effectivelycooled down during operation. As mentioned earlier, special care has tobe taken to ensure that the copper-based material from the heatdissipating core 32″ is not drawn or pulled to an exterior side surfaceof the electrode, as that could create an unwanted sparking site at thatlocation. In a first portion 80″ of the thermal coupling zone, atruncated axial end 84″ of the heat dissipating core 32″ has beenabsorbed into the thermal coupling zone. Portions of the truncated axialend 84″ may also be absorbed and intermixed with other materials in asecond portion 82″ as well. In this example, the electrode tip 34″ isbuilt on the severed end of the electrode body 36″ such that preciousmetal-based powder is directly melted into exposed portions of theelectrode base 30″ and exposed portions of the heat dissipating core32″. This is possible with the additive manufacturing process describedherein, which creates a weldless joint between the electrode tip 34″ andthe electrode body 36″, but does not form a circumferential laser weld.

Turning now to FIG. 8 , there is a flowchart showing the steps of anadditive manufacturing process 100 (sometimes referred to as a 3Dprinting process) that may be used to create the spark plug electrodedescribed herein. According to this example, additive manufacturingprocess 100 uses a powder bed fusion technique to form the electrode tip134 on the electrode base 130, as illustrated in the progressive stepsshown in FIGS. 9-12 . It should be appreciated, however, that additivemanufacturing process 100 may be used with any of the electrodes taughtherein, as well as others, and is certainly not limited to theillustrated example.

Starting with step 102, an electrode body 136 is provided with a heatdissipating core 132 at least partially surrounded by or encapsulatedwithin an electrode base 130. As explained in connection with FIGS. 5-7, an electrode body may be provided with one of a number of differentconfigurations, including: those where the heat dissipating core isretracted within the electrode base so that it does not reach an axialend of the electrode base (e.g., see FIG. 5 ); those where the heatdissipating core terminates at or near the axial end of the electrodebase (e.g., see FIG. 6 ); or those where the electrode body has beensevered or cut through the electrode base and the heat dissipating coresuch that an imaginary axial end of the core extends beyond the axialend of the electrode base and leaves a portion of the core exposed(e.g., see FIG. 7 ), to site a few possibilities. This last possibilityis further illustrated in FIG. 9 , where a truncated axial end 154 ofthe heat dissipating core 132 is exposed and is generally flush with anaxial end 160 of the electrode base 130. It should be appreciated thatany suitable method for cutting, severing or terminating the electrodebody may be used, including mechanical cutting or shearing, abrasivecutting, water jet or laser cutting, or some other suitable method forremoving the end of the electrode body.

Next, the electrode body 136 is secured within a tool or jig such thatthe electrode base 130 and/or the heat dissipating core 132 are exposedat a firing end 120, step 104. It is preferable that the electrode body136 be secured or mounted vertically within the tool such that thefiring end 120 is facing upwards. Any number of different tools andfixturing arrangements may be used for this purpose, including thosehaving horizontal build plates that are flush or nearly flush with theaxial end 160 and are designed to receive a thin powder bed.

Once secured within the tool, the firing end 120, with the exposedelectrode base and/or heat dissipating core portions, is covered with athin powder bed layer 128 that includes a first mixture of preciousmetal-based material, step 106. The first mixture may include preciousmetal-based material with no more than 60 wt % iridium (e.g., Pt—Ir40,Pt—Ir50, Ir—Pt40, Ru—Rh5, etc.), and preferably with no more than 50 wt% iridium (e.g., Pt—Ir40, Pt—Ir50, Ru—Rh5, etc.), although this is notrequired. In one example, the powder bed layer 128 has a thickness ofbetween 5 μm and 60 μm, inclusive, and more preferably a thickness thatis between 10 μm and 20 μm, inclusive.

Next, a laser or electron beam is used to melt or at least sinter thethin powder bed layer 128 covering the firing end 120, step 108. Anyreferences herein to “lasers” should be understood to broadly includeany suitable light or energy source including, but not limited to,electron beams and lasers; the same applies to “laser depositionlayers,” which broadly includes deposition layers created by anysuitable light or energy source including, but not limited to, thosecreated by electron beams and lasers. As illustrated in FIG. 10A, alaser L is generally aligned with the center axis A of the electrode andis directed towards the firing end 120 (which, in this example, includesexposed portion 160 of the electrode base 130 and exposed portion 154 ofthe heat dissipating core 132) such that it melts or sinters a thinpowder bed layer 128 as the laser traverses or moves across the axialend surface of the firing end; this is part of the powder bed fusionprocess. This forms an initial laser deposition layer 162 and begins toform different portions of a thermal coupling zone 138, which willestablish a direct thermal connection between an electrode tip 134 and aheat dissipating core 132 when the additive manufacturing process iscomplete.

According to one example, step 108 does not use a constant or uniformenergy level for the laser when melting the thin powder bed layer,rather it selectively controls the energy level according to anon-uniform energy profile so that more energy is concentrated towardsthe center of the firing end 120. FIG. 10B is an end or top view of thefiring end 120, with the different circular or annular zonesrepresenting different laser energy levels of the non-uniform energyprofile. For instance, zone 140 is a circular zone that encompassescenter axis A and is located at the middle of the firing end. In zone140, the laser energy is the highest level used during the non-uniformenergy profile and can be between 90% and 100% of a maximum orpredetermined energy level. Zone 142 is an annular zone thatconcentrically surrounds zone 140 and, according to this example,applies a laser energy level that is slightly lower than that applied inzone 140, such as between 75% and 90% of the maximum or predeterminedenergy level. Zone 144 is also an annular zone and it concentricallysurrounds zones 140, 142 so that it is located towards a radially outersection of the firing end 120. For zone 144, a laser energy level ofless than 75% of the maximum or predetermined energy level may be used;the lower energy level reduces the chances of drawing too much copper-and/or nickel-based material towards the sides of the electrode.Furthermore, by concentrating more laser energy towards the center ofthe firing end 120, the non-uniform energy profile is able to melt morematerial in the middle of the electrode body, including copper-basedmaterial from the heat dissipating core 132, nickel-based material fromthe electrode base 130, and precious metal-based material from the thinpowder bed layer 128. This deeper penetration in the middle of theelectrode body helps build the shape of the thermal coupling zone 138without drawing copper-based materials to the sides of the electrodewhere they could become unwanted sparking locations, as can be the casewith circumferential laser welds.

It is possible for the method to vary the laser energy distributionevery pass or every so many passes in order to control or at leastinfluence the size, shape and/or composition of the thermal couplingzone 138. With reference to FIGS. 11A-11B, there are respectively showna sectional view of the electrode body 136, and a top view of the firingend 120 with different circular or annular zones representing differentlaser energy levels. Again, the non-uniform energy profile mayconcentrate laser energy towards the center of the firing end 120 sothat the thermal coupling zone 138 reaches deeper and deeper into theheat dissipating core 132 each time a new laser deposition layer 164 isadded. For instance, the non-uniform energy profile may include zone150, which is a circular zone that encompasses center axis A at themiddle of the firing end 120, and can have a laser energy level between80% and 90% of a maximum or predetermined level. Zone 152, which is aconcentric annular zone encompassing the remainder of the axial end 160,may have a laser energy level of approximately 80% of a maximum orpredetermined level. During the repeat cycling of steps 106-108, themethod not only builds up the electrode tip 134 with a number of stackedlaser deposition layers, it may also vary or modulate the laser energyacross the firing end 120 according to the non-uniform energy profile inorder to create a customized thermal coupling zone 138 with first andsecond portions 180, 182. The first portion 180 is located deeper in theelectrode body 136 (i.e., further from the axial end 160) and is moreconcentrated towards the center of the electrode body, whereas thesecond portion 182 is located closer to the firing end 120 and is morespread out so that it is largely underneath the electrode tip 134. Thefirst portion 180 helps form the main thermal channel or conduit betweenthe electrode tip 134 and the heat dissipating core 132. It should beappreciated that the depictions of the first and second portions 180,182 are for purposes of illustration and that the actual portions mayhave different shapes and sizes than those shown.

On a last pass through, the method forms a final laser deposition layer166, which constitutes at least part of a sparking surface of theelectrode tip 134. When forming the final laser deposition layer(s) 166,the method may use a uniform energy profile or distribution, instead ofa non-uniform energy profile, in order to help smooth out or provide amore uniform sparking surface, as illustrated in FIGS. 12A-B. In thisexample, a single circular zone 156 may be used across the entire firingend 120 so that the final laser deposition layer(s) 166 is formed at aconstant laser energy level (e.g., a level of about 80% of a maximumenergy level). By using a constant laser energy level for the last cycleor several cycles of the method, an electrode tip 134 with a flattersparking surface 168 can be formed. Of course, the preceding descriptionis only one example of an additive manufacturing process that may beused, as other such processes are certainly possible. Specificparameters, such as the size, shape, number and energy level of thedifferent laser energy zones, may vary from the non-limiting examplesprovided herein.

The cycle or sequence of steps 106-108 is repeated until the methoddetermines that no more laser deposition layers are needed (i.e., theelectrode tip 134 has achieved the desired height). If step 110determines that more laser deposition layers are needed, then the methodloops back and repeats steps 106 and 108 so that a new laser depositionlayer can be built on top of the previous layer(s). It should beappreciated that on an initial pass or cycle through steps 106-108, step106 may cover the axial end 160 and truncated axial end 154 with a thinpowder bed 128 (i.e., the precious metal-based material of the thinpowder bed may be in direct contact with the nickel-based material ofaxial end 160 and the copper-based material of truncated axial end 154)and step 108 may melt or sinter the thin powder bed directly into ends160 and/or 154. In subsequent passes or cycles through steps 106-108,after the initial laser deposition layer 162 has already been formed,step 106 may apply the thin powder bed 128 so that it covers one or morepreviously created laser deposition layer(s) 162, as opposed to coveringthe actual surfaces of ends 160 and/or 154. In this example, step 108melts or sinters the thin powder bed material into the previouslycreated laser deposition layer(s), as well as possibly into theelectrode itself (depending on how thick the previously created laserdeposition layer(s) are and how deep the melting or sintering stepgoes). In both instances (i.e., in the initial pass and in subsequentpasses of steps 106-108), step 106 covers the firing end 120 with a thinpowder bed and step 108 melts or sinters the thin powder bed into thefiring end 120.

Since each laser deposition layer is formed first by melting orsintering powder from the thin powder bed and then allowing the materialto solidify, it is possible to adjust or modify the composition of thedifferent laser deposition layers by changing the composition of thepowder bed along the way. This enables the present electrode to have atailored or customized composition gradient across the thermal couplingzone 138 and/or the electrode tip 134 that spreads out differences inthermal coefficients of expansion, as opposed to having the fulldifference of those coefficients experienced at a single inter-layerboundary. For instance, on the second or a later pass through themethod, step 106 may cover the firing end 120 with a second mixture ofprecious metal-based material having a different composition than thefirst mixture (e.g., the second mixture may have a greater proportion ofprecious metal-based material), although this is not required.

Once step 110 determines that no additional laser deposition layers areneeded (i.e., the electrode tip 134 is fully formed by additivemanufacturing, the method progresses to step 112, where the spark plugelectrode or workpiece is removed from the tool. Skilled artisans willappreciate that the additive manufacturing process just described may beused to manufacture large numbers of electrodes at a time (i.e., batchprocessing), as well as various types of electrodes that differ fromthose shown here. One difference between the spark plug electrodeproduced according to the aforementioned process is that the electrodetip is securely fastened to the electrode base without the use of acircumferential laser weld (i.e., the present electrode has a weldlessjoint between the electrode tip and base), which is advantageous for anumber of reasons, including those described above.

It is to be understood that the foregoing is a description of one ormore preferred exemplary embodiments of the invention. The invention isnot limited to the particular embodiment(s) disclosed herein, but ratheris defined solely by the claims below. Furthermore, the statementscontained in the foregoing description relate to particular embodimentsand are not to be construed as limitations on the scope of the inventionor on the definition of terms used in the claims, except where a term orphrase is expressly defined above. Various other embodiments and variouschanges and modifications to the disclosed embodiment(s) will becomeapparent to those skilled in the art. For example, the exact size,shape, composition, etc. of a thermal coupling zone covered could varyfrom the disclosed examples and still be covered by the presentapplication (e.g., micrographs of actual parts could appearsubstantially different from the illustrated drawings, yet still becovered). All such other embodiments, changes, and modifications areintended to come within the scope of the appended claims.

As used in this specification and claims, the terms “for example,”“e.g.,” “for instance,” “such as,” and “like,” and the verbs“comprising,” “having,” “including,” and their other verb forms, whenused in conjunction with a listing of one or more components or otheritems, are each to be construed as open-ended, meaning that that thelisting is not to be considered as excluding other, additionalcomponents or items. Other terms are to be construed using theirbroadest reasonable meaning unless they are used in a context thatrequires a different interpretation.

What is claimed is:
 1. An additive manufacturing process formanufacturing a spark plug electrode, comprising the steps of: providingan electrode body that includes an electrode base and a heat dissipatingcore that is at least partially surrounded by the electrode base;covering a firing end of the electrode body with a thin powder bed layerthat includes a precious metal-based material; directing a laser or anelectron beam at the firing end of the electrode body such that it meltsor sinters at least some of the thin powder bed layer; and repeating thecovering and directing steps for a plurality of cycles so that anelectrode tip with a plurality of laser deposition layers and a sparkingsurface is formed on the electrode base and so that a thermal couplingzone is formed at least partially between the electrode tip and the heatdissipating core, wherein the thermal coupling zone directly thermallycouples the electrode tip to the heat dissipating core.
 2. The additivemanufacturing process of claim 1, wherein the providing step furthercomprises providing an electrode body that includes an electrode basehaving a nickel-based material and a heat dissipating core having acopper-based material or a silver-based material.
 3. The additivemanufacturing process of claim 1, wherein the providing step furthercomprises providing an electrode body that is part of a center electrodefor an industrial plug and includes a diameter at the firing end that isbetween 1.4 mm and 4.2 mm, inclusive.
 4. The additive manufacturingprocess of claim 1, wherein the providing step further comprisesproviding an electrode body that is part of a center electrode for anautomotive plug and includes a diameter at the firing end that isbetween 0.7 mm and 3.0 mm, inclusive.
 5. The additive manufacturingprocess of claim 1, wherein the providing step further comprisesproviding an electrode body that includes a heat dissipating core havinga single-material core that includes a thermally conductive material. 6.The additive manufacturing process of claim 1, wherein the providingstep further comprises providing an electrode body that includes a heatdissipating core having a multi-material core with an inner heatdissipating core component and an outer heat dissipating core component,the outer heat dissipating core component at least partially surroundsthe inner heat dissipating core component and includes a thermallyconductive material.
 7. The additive manufacturing process of claim 1,wherein the providing step further comprises providing an electrode bodythat includes an electrode base and a heat dissipating core that isretracted within the electrode base so that an axial end of the heatdissipating core does not reach an axial end of the electrode base, andthe covering step further comprises covering a firing end of theelectrode body with a thin powder bed layer so that, during an initialcycle, the thin powder bed layer only contacts the axial end of theelectrode base.
 8. The additive manufacturing process of claim 1,wherein the providing step further comprises providing an electrode bodythat includes an electrode base and a heat dissipating core with anaxial end that terminates at or near an axial end of the electrode base,and the covering step further comprises covering a firing end of theelectrode body with a thin powder bed layer so that, during an initialcycle, the thin powder bed layer contacts the axial end of the electrodebase and/or the axial end of the heat dissipating core.
 9. The additivemanufacturing process of claim 1, wherein the providing step furthercomprises providing an electrode body that includes an electrode baseand a heat dissipating core that has been severed or cut through theheat dissipating core so that an imaginary axial end of the heatdissipating core extends beyond an axial end of the electrode base, andthe covering step further comprises covering a firing end of theelectrode body with a thin powder bed layer so that, during a firstcycle, the thin powder bed layer contacts the axial end of the electrodebase and a truncated axial end of the heat dissipating core.
 10. Theadditive manufacturing process of claim 9, wherein, following theproviding step but before the covering step of the initial cycle, thetruncated axial end of the heat dissipating core is exposed and isgenerally flush with the axial end of the electrode base.
 11. Theadditive manufacturing process of claim 1, wherein the directing stepfurther comprises directing a laser or an electron beam at the firingend of the electrode body as part of a powder bed fusion process sothat, during an initial cycle, an initial laser deposition layer isformed and, during subsequent cycles, the thermal coupling zone isformed.
 12. The additive manufacturing process of claim 1, wherein thedirecting step further comprises directing a laser or an electron beamat the firing end of the electrode body as part of a powder bed fusionprocess so that, during a final cycle, a final laser deposition layer isformed with a uniform energy profile.
 13. The additive manufacturingprocess of claim 1, wherein the directing step further comprisesdirecting a laser or an electron beam at the firing end of the electrodebody and driving the laser or the electron beam according to anon-uniform energy profile.
 14. The additive manufacturing process ofclaim 13, wherein the non-uniform energy profile results in a first zonelocated at a middle of the firing end and a second zone that surroundsthe first zone, the laser energy level in the first zone is higher thanin the second zone such that more energy is concentrated towards themiddle of the firing end.
 15. The additive manufacturing process ofclaim 14, wherein the non-uniform energy profile further results in athird zone located towards a radially outer section of the firing endsuch that the third zone surrounds the second zone.
 16. The additivemanufacturing process of claim 13, wherein the non-uniform energyprofile helps create a customized thermal coupling zone that includes afirst portion that is located deeper in the electrode body and isconcentrated towards a middle of the electrode body, and a secondportion that is located closer to the electrode tip and is more spreadout so that it is largely underneath the electrode tip.
 17. The additivemanufacturing process of claim 1, wherein the directing step furthercomprises directing a laser or an electron beam at the firing end of theelectrode body such that it melts at least some material from the thinpowder bed layer, the electrode base and the heat dissipating core tocreate a thermal coupling zone alloy.
 18. The additive manufacturingprocess of claim 1, wherein the repeating step further comprisesrepeating the covering and directing steps for a plurality of cycles sothat the thermal coupling zone reaches deeper into the electrode bodyeach time a new laser deposition layer is formed.
 19. An additivemanufacturing process for manufacturing a spark plug electrode,comprising the steps of: providing an electrode body that includes anelectrode base and a heat dissipating core that is at least partiallysurrounded by the electrode base, whereby the electrode body is severedor cut through the heat dissipating core so that an axial end of theelectrode base and a truncated axial end of the heat dissipating coreare exposed; during an initial cycle, covering a firing end of theelectrode body with an initial thin powder bed layer that includes aprecious metal-based material, the initial thin powder bed layercontacts the axial end of the electrode base and the truncated axial endof the heat dissipating core; during the initial cycle, directing alaser or an electron beam at the firing end of the electrode body suchthat it melts or sinters at least some of the initial thin powder bedlayer and portions of the electrode base and the heat dissipating core,and causing the melted or sintered materials to at least partiallysolidify into an initial laser deposition layer; during a subsequentcycle, covering the firing end of the electrode body with a thin powderbed layer that includes a precious metal-based material, the thin powderbed layer contacts a previously formed laser deposition layer; duringthe subsequent cycle, directing the laser or the electron beam at thefiring end of the electrode body such that it melts or sinters at leastsome of the thin powder bed layer and portions of the previously formedlaser deposition layer, and causing the melted or sintered materials toat least partially solidify into a newly formed laser deposition layer;and repeating the covering and directing steps of the subsequent cycleso that an electrode tip with a plurality of laser deposition layers anda sparking surface is formed on the electrode base, wherein theelectrode tip is directly thermally coupled to the heat dissipatingcore.
 20. The additive manufacturing process of claim 19, wherein theelectrode tip is directly thermally coupled to the heat dissipating corewith a thermal coupling zone that includes a thermal coupling zone alloyhaving copper or silver from the heat dissipating core, nickel from theelectrode base, and at least one of iridium, ruthenium, or platinum fromthe electrode tip.